1. Field of the Invention
The present invention generally relates to a light source and a method of controlling the same. More specifically, the invention relates to an illumination system adapted to a projection apparatus and an illumination control method.
2. Description of Related Art
Conventionally, a projection apparatus provides color images with an illumination system sequentially emitting a red light beam, a green light beam, and a blue light beam to a light valve of the projection apparatus. This allows the projection apparatus to sequentially project red, green, and blue images onto a viewing screen. When red, green, and blue images appear rapidly in succession, due to visual retention in the human eyes, red, green, and blue images mix to form color images. Hence, the conventional projection apparatus provides color images in the above-described fashion.
A conventional illumination system uses an ultra high pressure (UHP) lamp to provide a white light beam and to transmit the white light beam through a rotating color wheel. An example of the color wheel includes an annular filter including red, green, and blue fan-shaped filters. Therefore, white light beams transmitted through the rotating color wheel are sequentially converted into red, green, and blue color light beams, respectively.
However, when the boundaries of different color filters move into the illumination region of the white light beam, i.e. during a spoke time, the white light beam is converted into two different color light beams. Consequently, incorrect colored light beams are transmitted to the light valve and thereby affecting the color accuracy of the images projected onto a viewing screen. For instance, U.S. Patent Application Publication No. 20060002109 disclosed that by continually transmitting white light beams through the color wheel, the white light beams pass through boundaries of different color fan-shaped filters.
U.S. Pat. No. 5,774,196 disclosed shutting off the spatial light modulator (SLM) during the spoke time. Although shutting down the SLM during the spoke time may help to improve the accuracy of the colors displayed on the viewing screen, dark images may be not dark enough, and thus the contrast of the projected images may deteriorate substantially since the light source is still in operation during the shut-off of the SLM. Moreover, a substantial amount of light energy provided by a light source is wasted due to maintaining the on-state of the light source when shutting off the SLM.
On the other hand, Taiwan Patent Publication Nos. 200729148 and 200729149 disclosed shutting off and turning on a light source at various light valve conditions. Although doing so saves energy, neither of the disclosures provides methods for substantially improving the accuracy of the displayed colors during the spoke time.